President Obama, first lady Michelle Obama and former presidents Jimmy Carter and Bill Clinton at the March on Washington 50th anniversary celebration.

If Rev. Martin Luther King Jr. had seen 50 years into the future, he might have been tempted to add "Democrats and Republicans" to the historically antagonistic pairings — "black men and white men, Jews and Gentiles, Protestants and Catholics" — who, in his "I Have A Dream" speech, would one day hold hands and sing, "Free at last."

The parties have seldom seemed so far apart as they did Wednesday, on the 50th anniversary of King's speech and the March on Washington. Not a single Republican elected official spoke at the "Let Freedom Ring" event at the Lincoln Memorial, site of King's 1963 speech, though some were invited.

House Speaker John Boehner of Ohio attended an earlier march commemoration on Capitol Hill, and House Majority Leader Eric Cantor of Virginia was traveling in Ohio and North Dakota, according to reports explaining why they had declined invitations. Former President George W. Bush was invited by event organizers, but declined because of recent heart surgery.

Whatever the reasons, the absence of any prominent past or present Republican official in a speaking role at the commemoration is unlikely to help the party's outreach to minorities. The hulking marble presence of the first Republican president, Abraham Lincoln, didn't really make up for the absence of living, breathing GOP officials.

So instead of a bipartisan celebration of one of the 20th century's greatest speeches and one of the most significant demonstrations in U.S. history, the event sometimes took on the feel of a Democratic National Convention. It seemed like just one more stop on the polarization express.

President Obama was joined by former presidents Bill Clinton and Jimmy Carter. John Kennedy and Lyndon B. Johnson were represented by daughters.

The Democratic Party's domination of the event didn't necessarily mean everything the main speakers said wouldn't or couldn't attract bipartisan support.

Obama, among others, spoke to how much the nation has changed for the better since the bad old days of 1963. That's certainly a point Republicans make, too.

The very fact that someone who looks like Obama is president is, of course, potent evidence of how much we've changed as a nation.

"Because they marched, city councils changed and state legislatures changed and Congress changed and, yes, eventually the White House changed," he said, speaking of the debt owed to the civil rights generation.

But the three Democratic presidents all cited varying parts of the Democratic bill of particulars against Republicans, without mentioning the other party by name.

They each singled out GOP-inspired voter ID laws, with Clinton delivering perhaps the best soundbite. "A great democracy does not make it harder to vote than to buy an assault weapon," he said to cheers.

The 50th anniversary of the march was a reminder of how completely the major parties have realigned along regional and racial lines since 1963. And much of that realignment, ironically, had everything to do with King and his fellow marchers getting the federal action they sought.

The same civil rights legislation that passed in 1964 and 1965, prohibiting discrimination in public accommodations and voter registration, helped to drive many whites to the Republican Party.

At the time of the 1963 march, there were moderate Republican leaders who publicly supported the civil rights movement. The Democratic coalition created by Franklin D. Roosevelt of Northern blue-collar whites, Southern rural whites and urban African-Americans, was intact, if fraying.

As Lyndon Johnson ruefully predicted, however, the Democratic Party would lose white Southerners, who have become a mainstay of the Republican Party.

Meanwhile, once Southern blacks were finally able to exercise their right to vote, they bonded to the party they viewed as most protective of those rights. That's made them an indispensable voting bloc for any Democrat with presidential aspirations who hopes to win enough primaries to gain the nomination.

Carter acknowledged as much on Wednesday in speaking of himself, Obama and Clinton:

"I realize that most people know that it's highly unlikely that any of us three ... would have served in the White House or be on this platform had it not been for Martin Luther King Jr. and his movement and his crusade for civil rights," said Carter. "So we are grateful to him for us being here."

At another point, Carter recalled the electoral boost he got from photo ops with the civil rights icon's wife, Coretta, and his father, Martin Luther "Daddy" King Sr.:

"I was really grateful when the King family adopted me as their presidential candidate in 1976. Every handshake from Dr. King, from Daddy King, every hug from Coretta got me a million Yankee votes."

That was the same Daddy King who had voted for the party of Lincoln up until 1960, when then-presidential candidate JFK called King's daughter-in-law, Coretta King, to express his concern for her husband, jailed for civil rights activism.

The elder King embodied that shift in party coalitions no less than Strom Thurmond, the Democratic senator from South Carolina who switched to the Republicans in 1964.

Wednesday, ironically, was the 56th anniversary of the Thurmond's record-setting anti-civil rights filibuster in 1957, a time when he led the segregationist forces in Congress.